The process of curing of large thick composite parts needs attention regarding the formation of residual stresses. Similarly, novel reactive thermoplastics need investigating to produce an efficient thermal cure profile that decreases the risk of warpage and residual stress. In this work, the polymerization kinetics of the Elium resin system is investigated by differential scanning calorimetry (DSC) tests, the analysis of thermo-grams, and the parameters of Kamal and Sourour’s semi-empirical model. A numerical model based on finite elements was set up to reproduce the temperature fields during part consolidation. Several processing conditions were investigated (dwell temperature, environment, heat exchange) in order to predict the thermal gradient within the part. The optimal cure profile was identified as a function of process parameters with the aim of minimizing the thermal gradient within the composite element. The analysis revealed that, for the reactive thermoplastic Elium, the consolidation in facilities with high thermal exchange may increase the risk of residual stresses within the parts, erasing the advantage of short cure cycles.

The use of interleaving material with viscoelastic properties is one of the most effective solutions to improve the damping capacity of carbon fibre-reinforced polymer (CFRP) laminates. Improving composite damping without threatening mechanical performance is challenging and the use of nanomaterials should lead to the target. In this paper, the effect of a nanostructured interlayer based on graphite nanoplatelets (GNPs) on the damping capacity and fracture toughness of CFRP laminates has been investigated. High-content GNP/epoxy (70 wt/30 wt) coating was sprayed on the surface of CF/epoxy prepregs at two different contents (10 and 40 g/m²) and incorporated at the middle plane of a CFRP laminate. The effect of the GNP areal weights on the viscoelastic and mechanical behaviour of the laminates is investigated. Coupons with low GNP content showed a 25% increase in damping capacity with a trivial reduction in the storage modulus. Moreover, a reduction in interlaminar shear strength (ILSS) and fracture toughness (both mode I and mode II) was observed. The GNP alignment and degree of compaction reached during the process were found to be key parameters on material performances. By increasing the GNP content and compaction, a mitigation on the fracture drop was achieved (−15%).

The use of interleaving material with viscoelastic properties is one of the most effective solutions to improve the damping capacity of CFRP laminates. Improving composite damping without threatening mechanical performance is challenging and the use of nanomaterials should lead to the target. In this paper, the effect of a nanostructured interlayer based on Graphite Nanoplatelets (GNPs) on the damping capacity and fracture toughness of CFRP laminates has been investigated. High-content GNP/Epoxy (70wt/30wt) coating was sprayed on the surface of CF/Epoxy prepregs at two different areal weight (10 and 40 g/m2) and incorporated at the middle-plane of a CFRP laminate. The effect of the GNP areal weight on viscoelastic and the mechanical behaviour of the laminates was investigated. Coupons with low-areal weight GNP interlayer showed a 25% increase in damping capacity with a trivial reduction of the elastic modulus. Moreover, a reduction in interlaminar shear strength (ILSS) and fracture toughness (both mode I and mode II) was observed in the composites with GNPs interlayer. GNPs alignment and degree of compaction reached during process were found as key parameters on material performances. By increasing the areal weight a mitigation on the mechanical performances drop was achieved (-15%).

Re-introducing recycled carbon fibre (rCF) into the manufacturing value chain significantly reduces environmental impacts. The fabrication of nonwoven mats made by carding rCF with thermoplastic filaments enables the production of preform suitable for manufacturing and thermoforming structural parts and fusion bonding technologies. The induction welding process takes advantage of the random nature of such materials since the discontinuous fibres contribute to the formation of microcircuits heated by the eddy currents related to the magnetic field, enabling a susceptor-less welding process. In this paper, the process window for the induction welding of rCF/MAPP laminates is screened. The compression-moulded laminates have been consolidated and experimentally characterised for comparison with welded joints. The quality of the bond is governed by the process parameters investigated, namely generator power, coil distance, translation speed and compaction load. The best-performing condition yielded an interlaminar shear strength of 11.7 ± 0.6 MPa, at least equal to that of the parent laminate. A Mode I initiation toughness of 560 ± 207 J/m² was measured, and all the joints failed cohesively. The uniformity of the conductive fibre network was identified as a likely controlling factor on the extent of the weld, based on the observed weld morphology and on literature evidence. Although the weld was not uniform across the configurations, the findings support induction welding as an effective joining method for rCF nonwoven laminates.

Re-introducing recycled carbon fibre (rCF) into the manufacturing value chain signifi-cantly reduces environmental impacts. The fabrication of nonwoven mats made by card-ing rCF with thermoplastic filaments enable the production of preform suitable for manu-facturing and thermoforming structural parts and fusion bonding technologies. The in-duction welding process takes advantage of the random nature of such materials since the discontinuous fibres contribute to the formation of microcircuits heated by the eddy cur-rents related to the magnetic field enabling a susceptor-less welding process. In this paper, the optimal welding parameters of induction welding of rCF/maleic anhy-dride-grafted polypropylene (MAPP) laminates are been investigated. The compression molded laminates have been consolidated and experimentally characterized for compari-son with welded joints. The strength and fracture behaviour of the welded joints are gov-erned by several process parameters, including generator power, coil distance, translation speed, and compaction load. The optimal condition yielded an interlaminar shear strength of 11.7 ± 0.6 MPa, at least equal to that of the parent laminate. A Mode I initiation tough-ness of 560 ± 207 J/m² was measured, and all the joints failed cohesively. The actual welded area inside the joint is function of the welding process. The uniformity of the conductive fibre network was found as the key parameter on the extent of the weld. Although the weld was not uniform across the configurations, the findings support in-duction welding as an effective joining method for rCF nonwoven laminates.

-Design optimization of filament wound cylinder by considering process induced residual stresses PALMIERI Barbara, BIANCHI Iacopo, DE PRISCO Nello, FORCELLE